This invention relates to cleaning of semiconductor wafers, including Germanium, Silicon and all other semiconductor compounds, such as Gallium Arsenide (xe2x80x9cGaAsxe2x80x9d) and Indium Phosphide (xe2x80x9cInPxe2x80x9d) and, more particularly, to a method and apparatus for thoroughly spray cleaning the surface of semiconductor wafers of particulate and organic contaminants in a manner that assures uniform and reproducible cleanliness of each wafer cleaned.
Semiconductor devices are typically fabricated on single crystal wafers of semiconductor materials using photo-lithographic mask and etch or ion-bombardment techniques. Typically the wafer contains a large number of semiconductor devices which are fabricated simultaneously. Initially, and at the completion of each step in the semiconductor fabrication process, some residue remains; the kind or type of residue being in part dependent on the stage of fabrication processing, and the wafer surface must be cleaned in preparation for a succeeding step. Depending upon the particular process step in the semiconductor device fabrication process being completed, the completion of a particular process step may incidentally also produce particulate debris, organic contaminants and/or unwanted pieces of thin film metallization layers on the surface of the semiconductor wafer. The residue, particulate debris, organic contaminants and metal pieces must be removed before proceeding with the next step in the fabrication process.
Mass produced semiconductors typically employ silicon technology and cleaning equipment exists to handle such mass production. Such cleaning equipment, however, is unsuited to semiconductors that use the III-V compounds identified in the Periodic Table of the Elements, such as InP and GaAs. First, cleaning solvents used for cleaning silicon wafers are either strong acids or strong bases, which are very harsh chemicals inappropriate for InP and GaAs wafers and produces a lower overall cleanliness. As an advantage, the present invention avoids harsh chemicals detrimental to the wafer. Second, the semiconductor chips produced on silicon wafers are not as fragile as the semiconductor chips fabricated on InP or GaAs wafers. Certain cleaning apparatus designed for cleaning of silicon wafers, such as brush scrubbing, produces structural damage when applied to cleaning of semiconductor devices constructed on InP or GaAs or other compound semiconductor wafers, especially for wafers containing gold metallization layers. As an advantage, the present cleaning system is less harmful mechanically to the semiconductor chips on the wafer.
Accordingly, a principal object of the invention is to clean wafers fabricated of compound semiconductors in a uniform and reproducible manner.
Another object of the invention is to clean Silicon and Germanium wafers or other types of substrates that employ devices or structures the could be damaged by application of conventional cleaning techniques.
A further object of the invention is to minimize and conserve the consumption of solvent and reduce the hazardous waste generated in the semiconductor cleaning process.
A still further object of the invention is to provide a computer controlled wafer cleaning apparatus that assures that each wafer cleaned is cleaned exactly alike.
And still another object of the invention is to provide an automated wafer cleaning apparatus that is relatively inexpensive to build and operate, may be constructed of xe2x80x9coff-the-shelfxe2x80x9d components, is easy to maintain, and may operate in an essentially unattended manner.
In accordance with the foregoing objects and advantages, semiconductor wafers are cleaned by moving a hydraulic broom about the surface of the wafer to sweep the wafer clean, the pressurized fluid issuing from the hydraulic broom being of a character that dissolves organic solvents as may be present on the surface of the wafer and produces the mechanical force to dislodge particulate debris from the wafer. In accordance with a specific aspect to the invention, the hydraulic broom is formed of an aspirated sprayer which combines gas released from a pressurized source of gas, suitably nitrogen, through a nozzle and aspirating the cleaning fluid, suitably acetone, through the nozzle into the gas stream providing a source of pressurized cleaning fluid expressed from the nozzle.
The cleaning system is automated. In one embodiment a three-axis positioner, under control of a programmed controller, controls the sweep of the hydraulic broom, moving the broom in a predefined xe2x80x9cscanningxe2x80x9d pattern over the wafer surface. As an advantage, the pattern of scan may be changed, the number of cleanings of an individual wafer may be changed, and the orientation of the wafer may be changed to permit a surface sweep in an alternate direction. In another embodiment polar movement is employed rotating the wafer while simultaneously continuously pivoting the broom over a predetermined arc about a pivot axis and linearly translating the position of that pivot axis.
The foregoing and additional objects and advantages of the invention together with the structure characteristic thereof, which was only briefly summarized in the foregoing passages, will become more apparent to those skilled in the art upon reading the detailed description of a preferred embodiment of the invention, which follows in this specification, taken together with the illustrations thereof presented in the accompanying drawings.